1. Field
At least some of the various embodiments are directed to radio frequency identification (RFID) readers and RFID tags utilizing a reduced number of interactions for the RFID reader to acquire some or all of the data payload of the RFID tags.
2. Description of the Related Art
In many circumstances a RFID reader may be in the presence of a plurality of RFID tags; however, the data payload of RFID tags is broadcast from the RFID tags one at a time to ensure the transmissions do not collide. In conventional systems the RFID reader and RFID tags perform a series of communications to isolate a single RFID tag (also known as selecting or singulating the RFID tag) to which the RFID reader then directly communicates to acquire the data payload of the tag. One such conventional system is Radio-Frequency Identity Protocols Class-1, Generation-2 UHF RFID Version 1.0.9 (also known as the EPCglobal RFID Air Interface) promulgated by EPCglobal Inc. Under the illustrative RFID Air Interface protocol, selecting a RFID tag involves the RFID reader broadcasting a “Query” command, which forces each RFID tag in communication range to generate a random slot counter value and to place the slot counter value in a register. Under this protocol a RFID tag may only communicate if its slot counter value is zero; thus, the RFID reader communicates with the RFID tag (if any) whose slot counter value is zero. Once communication with the RFID tag is complete, or if no RFID tag has a slot counter value of zero, the RFID reader issues a “QueryRep” command. Upon receipt of a “QueryRep” command, each RFID tag decrements its respective slot counter value and the process continues with the RFID tag (if any) that has a slot counter value of zero.
With respect to the RFID Air Interface protocol, consider as an example a situation where two RFID tags exist within the transmission range of a RFID reader. The RFID reader issues a “Query” command, which forces each RFID tag to generate a random number (between zero and three in this example), and places the number in its slot counter register. Further consider that a first RFID tag, after random number generation, has slot counter value of one and the second RFID tag has a slot counter value of two. Because neither RFID tag has a slot counter value of zero, neither RFID tag communicates to the RFID reader. The RFID reader, in turn, issues a “QueryRep” command, which forces the RFID tags to decrement their slot counter values. After the “QueryRep” command, the first RFID tag has slot counter value of zero, and the second RFID tag has slot counter value of one. The first RFID tag broadcasts a tag identifier (e.g. a 16 bit random number, which may also be referred to as a “handle” or “RN16”). The RFID reader returns an acknowledgement (by returning the tag identifier), and the first RFID tag then transmits some or all of the data payload (e.g. electronic product code or other data stored in the tag memory). At further command of the RFID reader, the first RFID tag may resend some or all the data payload, transition to a disabled or “killed” state, or update data payload contents with data supplied by the RFID reader, just to name a few actions that can be performed with respect to the tag. Once communication with the first RFID tag is complete, the RFID reader again issues a “QueryRep” command, forcing the second RFID tag to decrement its slot counter value. After the second illustrative “QueryRep” command, the second RFID tag has a slot counter value of zero, and thus the second RFID tag has been singulated and the RFID reader may communicate with the second RFID tag.
As shown by the above illustration, the slot counter values are not time periods in which a RFID tag is to respond, but instead merely define an order in which the RFID tags will be read. Stated otherwise, though a RFID tag operated under the illustrative RFID Air Interface protocol may know its place in line as defined by the slot counter value, the particular time at which the RFID tag is to transmit is unknown as the time is subject to the number of actions the RFID reader may need to perform on each previous RFID tag, and the number of gaps in the slot counter values among the RFID tags.
The illustration above is based on two RFID tags and only four possible slot counter values. However, in some situations there may be hundreds of RFID tags within communication range of a reader, and the slot values under the illustrative RFID Air Interface protocol may span as many as 16 bits (i.e., 65,536 values). Moreover, the illustrative RFID Air Interface protocol also defines multiple inventory rounds (each round a separate session for communication) and use of “inventory flags” on a per-session basis. The possible inventory rounds and flags dictate further interaction between the RFID reader and the RFID tags to establish/verify the inventory round and assert/de-assert the inventory flags. Thus, the process of singulating and communicating with each and every RFID tag in a population of RFID tags may require several thousand interactions, and dictates significant complexity in the design of RFID tags, particularly the RFID circuits within the RFID tags.